src/basic/replace-var.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2012 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <stddef.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24
  25 #include "alloc-util.h"
  26 #include "macro.h"
  27 #include "replace-var.h"
  28 #include "string-util.h"
  29
  30 /*
  31  * Generic infrastructure for replacing @FOO@ style variables in
  32  * strings. Will call a callback for each replacement.
  33  */
  34
  35 static int get_variable(const char *b, char **r) {
  36         size_t k;
  37         char *t;
  38
  39         assert(b);
  40         assert(r);
  41
  42         if (*b != '@')
  43                 return 0;
  44
  45         k = strspn(b + 1, UPPERCASE_LETTERS "_");
  46         if (k <= 0 || b[k+1] != '@')
  47                 return 0;
  48
  49         t = strndup(b + 1, k);
  50         if (!t)
  51                 return -ENOMEM;
  52
  53         *r = t;
  54         return 1;
  55 }
  56
  57 char *replace_var(const char *text, char *(*lookup)(const char *variable, void*userdata), void *userdata) {
  58         char *r, *t;
  59         const char *f;
  60         size_t l;
  61
  62         assert(text);
  63         assert(lookup);
  64
  65         l = strlen(text);
  66         r = new(char, l+1);
  67         if (!r)
  68                 return NULL;
  69
  70         f = text;
  71         t = r;
  72         while (*f) {
  73                 _cleanup_free_ char *v = NULL, *n = NULL;
  74                 char *a;
  75                 int k;
  76                 size_t skip, d, nl;
  77
  78                 k = get_variable(f, &v);
  79                 if (k < 0)
  80                         goto oom;
  81                 if (k == 0) {
  82                         *(t++) = *(f++);
  83                         continue;
  84                 }
  85
  86                 n = lookup(v, userdata);
  87                 if (!n)
  88                         goto oom;
  89
  90                 skip = strlen(v) + 2;
  91
  92                 d = t - r;
  93                 nl = l - skip + strlen(n);
  94                 a = realloc(r, nl + 1);
  95                 if (!a)
  96                         goto oom;
  97
  98                 l = nl;
  99                 r = a;
 100                 t = r + d;
 101
 102                 t = stpcpy(t, n);
 103                 f += skip;
 104         }
 105
 106         *t = 0;
 107         return r;
 108
 109 oom:
 110         free(r);
 111         return NULL;
 112 }